Allow an extension to add a file to the chat context

[DanaMartens]

Type: Feature Request

I need a way to programatically add a file to the chat context. For example, if a user right-clicks on text for an embedded image in a document and chooses a Suggest Alt Text command, I want to retrieve the image and use the visiona capability to suggest alt-text based on what is seen in the image. When I ask GitHub Copilot if this is possible, it suggests the following but it doesn’t work:

    await vscode.commands.executeCommand("workbench.action.chat.addFileToContext", imageUri);

VS Code version: Code 1.96.4 (cd4ee3b, 2025-01-16T00:16:19.038Z)
OS version: Windows_NT x64 10.0.26100
Modes: